If this fact makes you uneasy just know that 100% of the universe's galaxies, except the one we are currently in, are already unreachable within your lifetime.
If this fact makes you uneasy just know that (nearly) 100% of the galaxy's solar systems except the one we're currently in are (likely) unreachable within your lifetime.
Though to be fair, I think the original title can't possibly know this, for instance if we live in a simulation, what's to say that some sort of algorithm (assuming we learn to meta-code our own existence) could put us in any galaxy we choose... Or warp drives, worm holes... light speed travel hardly seems worth the trouble, and unfeasable.. but if we can master warp drives, and bending space around us... then is there a limit on max speeds? If we can actually reprogram the universe would there be anything we couldn't do? have any other alien civilizations realized that at all?
If we're in a simulation then there aren't any alien civilizations. No sense wasting computational resources on them.
P.S. As far as I know, computational complexity is the only physical quantity that doesn't obey conservation laws. So we're probably not in a simulation. If we were, it would probably be the other way around.
If we are in a simulation it’s most likely a physics/first-principles driven simulation… probably a “what if physics worked like $X” type of deal. So fidelity is likely the primary design goal and the weird nature of computational complexity in our universe is likely just an emergent property of the physics they setup the simulation with.
Not sure I agree about the overall information complexity, since a first principles physics simulation of a universe involves simulation of all the wave/quanta up through molecular dynamics and on to macroscopic behaviour of the universe (and us in it)…
It’s hard for me to imagine the “information complexity” we’re inducing into the universe as significant compared to the total size of the state machine representing all the neutrinos and photons in the universe, let alone the other particles.
Also if the the universe is a simulation it makes sense the simulators would be working with snapshots since even if you have the computational capabilities to simulate an entire universe, you probably don’t want to waste whatever time/energy resources exist in the simulating universe, simulating the first few billion years till your simulated universe gets to the point you’re most interested in, be it changing parameters / picking the outcome of particular random outcome or just zooming in and studying what goes on in the randomness, or just looking at it like some kind of highly advanced virtual zen garden.
So I’m not entirely convinced that our electronic computation devices which operate by way of the movement of electrons or photonics devices operating by manipulating photons (and usually electrons too), represents our hypothetical simulators having to design or run a simulation of anything beyond what we call “normal operating behaviour of clumps of solid baryonic matter”. All the computers in the world, full of electrons and interconnected by fibre optic lasers, is unlikely to involve simulating more electrons, neutrinos, and other subatomic particle interactions than are necessary to simulate the earth’s inner and outer core and their electrodynamic (which are coupled to the solar electrodynamics) and thus simulate the production of the earths magnetic field.
> If we're in a simulation then there aren't any alien civilizations. No sense wasting computational resources on them.
Seeing how mindbogglingly huge the universe is, our insignificant planet is unlikely to be the most intensive object to simulate. For a Universe simulator it would be peanuts, less than peanuts, peanut crumbs that fell behind the pantry where you can't clean them.
Think of it this way: it's trivially easy to randomly generate terrain for a video game world. The "size" of the in-game universe is just an arbitrary parameter.
Populating the world with interesting NPCs, is, however, a vastly more difficult problem than just scaling the same copy-pasted planets and stars across light years.
So no, the size of our universe is just a scale parameter. There's no evidence that it's more computationally complex out there than here, and computational complexity is the only interesting metric.
This assumes humans are interesting NPCs. I feel like we're the bizarre comic relief planet for the really interesting players to have the space adventure of the day.
I understand your point, though, but even if it was true, keeping track of all the physics in the Universe's filler would demand more processing power than what is needed for our planet. The speed of light would be our rendering depth, and that's still an unthinkable amount of computing, copy-paste included.
Why wouldn’t aliens work in a simulation model? The universe could be a shared sandbox to cross pollinate models or expose them to similar realities. Hah.
Nearly 100% of the countries on this very earth are unreachable to most poor humans within their lifetime.
And for a sizeable chunk of humans even reaching the very neighbourhood of their country, geography involves putting their lives on risk on a near sure to sink boat only to be shot/sent/sunk back by border police.
Humans are horrible at working together for their own good.
Everything is magic until we understand it. If one took a keychain flashlight back a few hundred years they might be burned as a witch. There are still tiny pockets of humans that believe if you take their picture, you are stealing their soul.
This is a really great question that embodies the hacker spirit of trying to find loopholes and edge cases. I'm not an expert, but I think the answer is that there are no half-reachable galaxies. If there is a galaxy that is only partially reachable, then it must eventually be torn apart by the expansion of the universe. We could theoretically send a ship to the reachable half, and if the galaxy was still in one piece, we could then take a quick jaunt from the reachable half to the unreachable half. So for the unreachable half to be actually unreachable, it would have to be far away from the reachable half. I'm guessing that all galaxies have strong enough gravity that they won't be torn apart by the expansion of the universe.
Reachable and visible are different things. There are plenty of galaxies that are visible, but not reachable. But I think a similar argument would apply to show that there are no half-visible galaxies. Light can certainly make it from one side of a galaxy to the other. If we can see the light emitted by the near side of the galaxy, then we can see light that originated on the far side of the galaxy and passed through the near side on its way to us. Both sets of photons will reach us, and both will have about the same redshift. The only difference will be that the the photons from the far side of the galaxy will be a few thousand years older than the near ones. (This is all ignoring the fact that we can see all the way back to the cosmic microwave background, which comes from a time in the universe's history when there were no galaxies at all. Anything we can see that looks like a galaxy isn't even on the visible/not-visible boundary!)
No. The proper boundaries are between galaxy clusters, which remain gravitationally bound to each other. If you can reach a cluster such that its gravity is strong than the expansion of the universe, then you can reach every part of that cluster.
Does the mean, that the cluster, that is going to become unreachable next is going to "become" unreachable in its entirety in a single unit of time (like maybe Plank time)?
To answer myself: yes. The clusters close to the outer event horizon are moving away from us at the speeds extremely close to the speed of light. Correspondingly from our standpoint of view their length along that direction is extremely contracted, and gets closer and closer to infinitesimally small as they get closer and closer to the horizon.
It's mind blowing to imagine that the observable universe is bigger than 90 billion light years, space-time expanding at multiple times the speed of light.
If expansion keeps accelerating, then at some point gravity won't be able to keep the local cluster together and even those galaxies will drift away, then star systems, then planets, then matter itself will be torn apart until atoms and particles and quarks are destroyed. A dark future awaits indeed.
Something in my mind tells me that there must be more to it, the careful balance of universal constants that allow for matter and stars and life to exist surely would not allow it all to be destroyed forever in the end...
> Something in my mind tells me that there must be more to it, the careful balance of universal constants that allow for matter and stars and life to exist surely would not allow it all to be destroyed forever in the end...
Keep in mind that we don't really understand this stuff.
"Dark matter" isn't a weird phase of matter, it's the name of the Keleven inserted because our observations of the universe don't match up with the theory. Ditto "dark energy."
The expansion of the universe is accelerating and we don't know why. If we don't know why, we don't know it isn't going to stop tomorrow, or reverse, or happen differently based on where you are in the universe. The things we've already observed about relativity and quantum mechanics are very counter-intuitive.
But at the same time, "I don't want it to" doesn't mean it's not going to happen. The arrow of time goes in one direction. We don't know how it ends until we get there.
> the careful balance of universal constants that allow for matter and stars and life to exist surely would not allow it all to be destroyed forever in the end...
Imagine a brute-force creation of x^y universes with varying cosmological constants. Surely some universes with the right ingredients for life also include a deep freeze or a Big Crunch.
Or, maybe our universe was created in a lab somewhere and they’re trying to figure out how to make a stable universe through experimentation. And we’re iteration #42.
What if our universal parameters don't make us much different than the universes with #41 being the answer and #43 being the answer... and of course the answer is guessed correctly in a satirical sci-fi in those respective universes. Just an infinite chain of universes where the initial variables determine the number/answer mentioned in one of Douglas Adam's books.
I saw a video proposing that it might be possible that the universe collapses on itself again and everything is reset.
But there are more non reversible things going on than just expansion. I only just found out that all elements radioactively decay and will eventually be gone.
Beyond OUR reach. I am sure extreme advanced civilization are capable of traveling 3-dimensional space without considering 4th dimension (time). Just like we can use video-recorder to record 3D world and put it on a 2D film to watch on a 2D screen, if advanced ET figured out ways to travel without consideration for time, then then switch from one point to another happens instantaneously. Whether its going from one room to another, or from one place in Universe to another, far far away. To them Einstein theories or articles like this one are just "thing of being a human-being".
I wonder if this is one aspect of The Great Filter that keeps aliens from contacting each other. 6% is still a lot to work with but shaving off 19 out of 20 galaxies sure helps explain a lot.
If you decided to travel to the furthest galaxies you could reach, at some point even they will move beyond the reach of Earth as space expands. To colonize them means to exile yourself from Earth permanently.
Traveling through an infinitely expanding universe is like traveling into a permanent headwind in every direction.
Weird question I just thought of: if space is always expanding, why aren't the objects around us, even their very atoms, getting slowly torn apart? Are the forces holding them together just constantly pulling them back together? Is it just a very small amount of expansion at a human scale? Does this affect very sensitive measurements of distance?
What if we're in a simulation, and algorithmically there's a way or method that will drop you in any coordinate at any time in the universe's timeline so that you can indeed explore space, and return home for dinner? I mean it'd require a TARDIS to exist probably lol, but in a sim, why not? Of course if we're in a sim, then that's probably not part of our overall 'goal' for creation, and likely we're the only creatures created so exploration really won't satisfy us, other than total galactic conquest, but then what?
When you stand next to somebody and you look at this person, through the expansion of the universe and the amount of time the light needs to travel from the surface of that person, to your eyes; means that when you see this person in the original distance, you do not see that person at the actual distance. It's not possible to share a contemporary timeline with other persons, everything is a few nano seconds delayed, you are existing in everybody else's past.
Thank you metagame for considering the philosophical and mathematical implications! Here's an (unpublished) proposal for a consistency proof that free will is finite.
Conway's Free Will Theorem: "if we have free will ... so must some elementary particles"
Infinity cannot be approximated with finite numbers (MIP* = RE "Prior to the new work, mathematicians had wondered whether they could get away with approximating infinite-dimensional matrices by using large finite-dimensional ones instead. Now, because the Connes embedding conjecture is false, they know they can’t.")
-> The future can never be perfectly preordained (Gisin "If numbers cannot have infinite strings of digits, then the future can never be perfectly preordained.")
Computers can only run recursive simulations, they can never actually reach infinity. The Turing Machine (cellular automaton Rule 110) can only expand to the limit of the tape.
Yet we can choose to surrender our free will to the greater good, and be part of the infinite pattern (cellular automaton Rule 90 Sierpinski Triangle). Rather than crystallising in ourselves, we should thank the root node, and thank others and love our neighbour, continuing the growth.
It takes me a while to write blog posts, but I have some rough notes about many topics: fractals especially the Sierpiński triangle, singing/reading/writing/listening/speaking/typing, therapeutic games, language invoking spirits, aunties dancing in parks to keep streets safe at night (via HN).
If you'd be willing to read those rough notes and tell me which categories are more interesting, that would help to prioritise the blog post writing! Like a good engineer, it's turning vague user requests into specific actionable requirements.
Here's the briefest of thoughts about litter and saving the environment:
• Love your neighbours the trees and birds. People first, but we are to steward God's creation. The ocean knows us only by our litter.
• While you go, clean now. "If not me, who? If not now, when?"
The expansion of space itself is not subject to the same constraints as travel through space.
Put another way: Nothing can travel through space faster than light. But the expansion of space itself isn’t a form of travel, and so it’s not subject to this limitation.
Expansion isn't objects in space moving farther apart through space it's the change in the geometry of space itself. A poor analogy might be a continuous zoom of a map map on your phone while something always moves less than a constant speed limit of pixels per second on the screen. It is easy to see this object can move around locations on the map but may not be able to reach most of the map if it is zooming in fast enough that far away portions !at get farther away faster than it can travel to them at the constant pixels per second.
"I point out that the often voiced claim that in the general theory of relativity (GR) geometry and gravity are ‘associated’ with each other can be understood in three different ways. The geometric interpretation asserts that gravity can be reduced to spacetime geometry, the field interpretation claims that the geometry of spacetime can be reduced to the behaviour of gravitational fields, and the egalitarian interpretation affirms that gravity and spacetime geometry are conceptually identified."
